Abstract. The aim of this study was to explore the effects of the bisphosphonate zoledronate on calcification induced by inorganic phosphate (Pi) and/or bone morphogenetic protein 2 (BMP-2) and the underlying mechanisms. Primary vascular smooth muscle cells (VSMCs) from rats were treated with 3 mM Pi or 3 mM Pi/BMP-2, with and without addition of zoledronate; 1.4 mM Pi served as a control. Calcium deposits, expression of core binding factor α-1 (Cbfa-1), osteopontin (OPN), parathyroid pituitary-specific transcription factor (Pit)-1 and Pit-2, and Pi uptake of VSMCs was determined. The calcification of VSMCs induced by elevated Pi or Pi/ BMP-2 was significantly inhibited by zoledronate. The expression of Cbfa-1, OPN and Pit-1 was increased significantly after treatment with an elevated level of Pi or Pi/BMP-2, and this expression was significantly suppressed by addition of zoledronate. Pi uptake of VSMCs increased following treatment with elevated Pi and significantly decreased by addition of zoledronate. These results indicated that zoledronate effectively inhibited calcification induced by Pi/BMP-2, and this may have been achieved by means of the downregulation of expression of calcification-related proteins and uptake of Pi.
IntroductionVascular calcification is highly prevalent and is a major contributor to cardiovascular disease (CVD) in patients with chronic kidney disease (CKD). Susceptibility to vascular calcification is in part genetically determined and actively regulated by diverse inducers and inhibitors. One of these inducers, hyperphosphatemia, promotes vascular calcification, and the control of arterial calcification is now recognized as a means to prevent CVD events in patients with CKD (1,2).Vascular calcification is an active, cell-mediated process that results from an imbalance between the promoters and inhibitors of mineralization (3,4). Several molecules that normally regulate osteoblast differentiation and bone formation have been found in calcifying vessels, such as osteonectin, osteocalcin, matrix Gla protein and bone morphogenetic protein 2 (BMP-2) (5-7). Elevated phosphate (Pi) levels also induce smooth muscle cell (SMC) calcification and osteogenic phenotypic modulation (8,9).Bisphosphonates (BPs) are widely used in the treatment of diseases associated with excessive osteoclast-mediated bone resorption, such as osteoporosis (10,11). The classical pharmacological effects of BPs appear to result from two key properties: their affinity for bone mineral and their inhibitory effects on osteoclasts. Mineral binding affinities differ among the clinically used BPs, and this may influence their differential distribution within bone, their biological potency and their duration of action (12,13). It is reported that ibandronate prevents experimentally induced arterial calcification in uremic rats (14). These findings extend the link between bone remodeling and vascular calcification of CKD, opening perspectives toward novel therapeutic strategies. However, whether zoledronate, a new third generati...